1. Field of the Invention
The present invention relates to light sources; and more specifically to a light-emitting diode (LED) lamp for producing a biologically-corrected light.
2. Background
Melatonin is a hormone secreted at night by the pineal gland. Melatonin regulates sleep patterns and helps to maintain the body's circadian rhythm. The suppression of melatonin contributes to sleep disorders, disturbs the circadian rhythm, and may also contribute to conditions such as hypertension, heart disease, diabetes, and/or cancer. Blue light, and the blue light component of polychromatic light, have been shown to suppress the secretion of melatonin. Moreover, melatonin suppression has been shown to be wavelength dependent, and peak at wavelengths between about 420 nm and about 480 nm. As such, individuals who suffer from sleep disorders or circadian rhythm disruptions continue to aggravate their conditions when using polychromatic light sources that have a blue light (420 nm-480 nm) component.
Curve A of FIG. 1 illustrates the action spectrum for melatonin suppression. As shown by Curve A, a predicted maximum suppression is experienced at wavelengths around about 460 nm. In other words, a light source having a spectral component between about 420 nm and about 480 nm is expected to cause melatonin suppression. FIG. 1 also illustrates the light spectra of conventional light sources. Curve B, for example, shows the light spectrum of an incandescent light source. As evidenced by Curve B, incandescent light sources cause low amounts of melatonin suppression because incandescent light sources lack a predominant blue component. Curve C, illustrating the light spectrum of a fluorescent light source, shows a predominant blue component. As such, fluorescent light sources are predicted to cause more melatonin suppression than incandescent light sources. Curve D, illustrating the light spectrum of a white light-emitting diode (LED) light source, shows a greater amount of blue component light than the fluorescent or incandescent light sources. As such, white LED light sources are predicted to cause more melatonin suppression than fluorescent or incandescent light sources. For additional background on circadian effects of light, reference is made to the following publications, which are incorporated herein by reference in their entirety:    Figueiro, et al., “Spectral Sensitivity of the Circadian System,” Lighting Research Center, available at: http://www.lrc.rpi.edu/programs/lightHealth/pdf/spectralSensitivity.pdf.    Rea, et al., “Circadian Light,” Journal of Circadian Rhythms, 8:20 (2010).    Stevens, R. G., “Electric power use and breast cancer; a hypothesis,” American Journal of Epidemiology, 125:4, pgs. 556-561 (1987).    Veitch, et al., “Modulation of Fluorescent Light: Flicker Rate and Light Source Effects on Visual Performance and Visual Comfort.
As the once ubiquitous incandescent light bulb is replaced by fluorescent light sources (e.g., compact-fluorescent light bulbs) and white LED light sources, more individuals may begin to suffer from sleep disorders, circadian rhythm disorders, and other biological system disruptions. One solution may be to simply filter out all of the blue component (420 nm-480 nm) of a light source. However, such a simplistic approach would create a light source with unacceptable color rendering properties, and would negatively affect a user's photopic response. What is needed is an LED light source with commercially acceptable color rendering properties, which produces minimal melatonin suppression, and thus has a minimal effect on natural sleep patterns and other biological systems.